Cavitation and flashing are both phenomena that occur in fluid systems and can cause damage to equipment and reduce system efficiency. While they are related, they are distinct phenomena:

1. Cavitation:

   • Cavitation is the formation and collapse of vapor bubbles or cavities within a liquid due to a rapid change in pressure.
   • When the pressure of a liquid drops below its vapor pressure, bubbles of vapor form within the liquid. These bubbles are carried along with the flow and can collapse when they encounter higher-pressure regions.
   • The collapse of these vapor bubbles near solid surfaces can generate intense shock waves and high-velocity microjets, causing erosion, pitting, and damage to components such as valves, pumps, and propellers.
   • Cavitation can also result in noise, vibration, and reduced performance of equipment.

2. Flashing:

   • Flashing, also known as vaporization or boiling, occurs when a liquid undergoes a rapid phase change from liquid to vapor due to a decrease in pressure.
   • This phenomenon typically occurs at or near the throat of a control valve or other restrictions in the flow path where the pressure drops suddenly.
   • Flashing is characterized by the formation of vapor bubbles within the liquid stream, leading to a mixture of liquid and vapor phases.
   • Similar to cavitation, flashing can cause erosion and damage to equipment and can also result in a loss of control and accuracy in flow measurement and control systems.

Causes of Cavitation and Flashing:

• Cavitation and flashing are primarily caused by changes in pressure and velocity within fluid systems.
• Cavitation often occurs in high-velocity flow regions or at points of sudden pressure drop, such as near pump impellers, control valves, or sharp bends in pipelines.
• Flashing typically occurs at the entrance to control valves, throttling devices, or other flow restrictions where the pressure drops rapidly, causing the liquid to boil or vaporize.
• Both phenomena can be exacerbated by factors such as high fluid velocities, low fluid temperatures, high fluid viscosity, and improper system design or operation.

To prevent cavitation and flashing, engineers often design fluid systems with gradual pressure changes, use anti-cavitation and anti-flashing trims in control valves, install flow straighteners or diffusers to reduce turbulence, and operate equipment within specified pressure and velocity limits.